Fracture Resistance of Thermal‐Mechanical Aged Resin Composite‐Restored Premolars: Effect of Different Application Protocols of a Universal Adhesive
Fereshteh Shafiei, Marzieh Moradian, Marziyeh Naseri MojaradABSTRACT
Objectives
This research investigated the effect of different applications of Universal bonding on the fracture resistance (FR) of maxillary premolars restored with mesio‐occluso‐distal resin composite.
Materials and Methods
One‐hundred and eight extracted maxillary premolars were randomly assigned into nine groups ( n = 12): (1) ST, sound teeth; (2) nonrestored teeth; (3) SEE, selective enamel etching; (4) E&R, etch‐and‐rinse; (5) SDE, selective dentin etching; (6) SEE+resin layer; (7) E&R+resin layer; (8) SDE+resin layer/precuring; (9) SDE+resin layer/co‐curing. Following restoration, mechanical loading (100,000 cycles, 50 N), 6‐month water storage, and thermocycling (1000 cycles), FR was tested. Failure mode was evaluated. Data were analyzed using one‐way ANOVA and Tukey test ( α = 0.05).
Results
SDE+resin layer/precuring showed the highest mean fracture load (1222.0 ± 58.7 N), with a significant difference with all groups ( p < 0.001), except SDE+resin layer/co‐curing (1166.5 ± 50.3 N). FR of SEE with the lowest value (894.50 ± 70.41 N) was lower than SDE ( p < 0.001) but comparable with E&R. Resin layer significantly improved FR in all etching conditions, except the E&R group ( p = 0.272). The highest number of restorable fractures was in two SDE with resin layer groups.
Conclusion
Adhesive application protocols affected FR. Combining short‐time dentin etching with a HEMA‐free hydrophobic resin may be suggested to increase the stable reinforcement potential of universal adhesive‐resin composite restorations in premolars and preserve teeth under high loading.
Clinical Relevance
The adhesive application protocol considerably affected the fracture resistance of MOD resin composite–restored premolars. A short time dentin etching using an ultra‐mild universal adhesive, along with increasing hydrophobicity of the adhesive interface, may enhance the mechanical reinforcement of resin composite‐restored premolars during simulated thermal‐mechanical intraoral conditions. This approach also possibly prevents the risk of catastrophic failure under unexpectedly high loads.